Molding system with integrated film heaters and sensors

ABSTRACT

Improved mold manifold and hot runner nozzle using thin film elements include at least one active or passive thin film element disposed along a melt channel between the manifold inlet and the hot runner nozzle. Preferably, the thin film element may comprise a thin film heater in direct contact with the molten resin and position to aid in the heat and flow management of the resin within the melt channel. Thin film temperature sensors, pressure sensors, and leak detectors may also be provided in the vicinity of the melt channel to enhance process control in the injection molding machine.

This application is a continuation of U.S. patent application Ser. No.10/187,331, filed Jul. 2, 2002, now U.S. Pat. No. 6,575,729 which is acontinuation of U.S. patent application Ser. No. 09/695,017, filed Oct.25, 2000, now abandoned, which is a continuation of U.S. patentapplication Ser. No. 09/550,639, filed Apr. 14, 2000, now U.S. Pat. No.6,341,954, which is a continuation of U.S. patent application Ser. No.09/096,388, filed Jun. 12, 1998, now U.S. Pat. No. 6,305,923.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an improvement in heat management andprocess control for a molding process and, more particularly, to the useof active and/or passive film heating and/or sensing elements locatedalong a flow channel of molten resin to a mold cavity space.

2. Description of the Related Art

In an injection molding process, it is important to maintain a resin ina molten state as it flows from a nozzle of an injection moldingmachine, through a mold sprue bushing, a mold manifold, a hot runnernozzle, and into a mold cavity space, where the resin cools to form aninjection-molded article. Additionally, the shear stress profile of theflow of resin must be monitored and managed to insure proper filling ofthe cavity space. This is especially important in the area close to themold gate because the temperature there is rapidly cycled between hotand cold conditions before the molded article is removed from thecavity. Temperature control issues are also very important when moldingcertain thermally-sensitive materials such as PET in a multicavity moldor when molding articles made of different materials that are injectedthrough a single hot runner nozzle. Accordingly, much effort has beendirected towards improving heat management and process control in theinjection molding process, particularly in the mold manifold and hotrunner nozzle. To date, several methods and means have been employedwith varying degrees of success. Included among the methods and meanscommonly employed are heat pipes, high frequency induction heaters,microwave heaters, ceramic heaters, infrared radiation heaters,electrical heaters, etc. Such electric heaters include coils, band, orcartridge heaters which are used to heat the molten resin inside thescrew barrel, in the machine nozzle, in the manifold, in the hot runnernozzle, and in the mold gate area.

U.S. Pat. No. 5,645,867 issued to Crank, et al. (incorporated herein byreference) illustrates the current state of the art with respect toheating the mold manifold. Crank, et al. teaches heating the manifold bydisposing infrared radiation heaters on an outer surface of themanifold. However, as is typical of such prior art manifold heatingapparatuses, a significant proportion of the heat generated by theheaters is wasted heating the entire manifold block rather than directlyheating the resin flowing in a melt channel contained therein.

U.S. Pat. No. 5,614,233 issued to Gellert (incorporated herein byreference) discloses a state of the art heater for a hot runner nozzle,in which a helical electrical heater is embedded in a spiral groove thatsurrounds the hot runner nozzle. The heater comprises a resistive wireenclosed in a refractory powder electrical insulating material such asmagnesium powder oxide. The helical portion of the heater ispress-fitted and reshaped into place in the spiral groove. However, thedisclosed heater heats both the hot runner nozzle body and the meltchannel contained therein, a relatively inefficient heating arrangement.Additionally, manufacturing the spiral groove and assembling the heatertherein is time-consuming and costly.

The foregoing problems with prior art heaters are particularly evidentin coinjection and multiinjection mold manifolds and hot runner nozzles.For example, U.S. Pat. No. 4,863,665 issued to Schad, et al.(incorporated herein by reference) discloses the use of a singleelectrical heater attached to the outer surface of a hot runner nozzleto heat three melt channels simultaneously. Schad, et al., however,faces several drawbacks. First, less heat is transmitted to the innerchannels than to the outer channels. Second, the heat supplied to eachchannel cannot be varied according to the size of each channel and theTheological characteristics of the resin flowing therein.

European Patent 312 029 B1 issued to Hiroyoshi (incorporated herein byreference) discloses a heater made of an insulating ceramic film that isflame-sprayed on the outer surface of the nozzle which introduces theresin into the molding machine. The heater may be a continuous areaheater completely covering the nozzle, a heater made of a plurality oflongitudinal strips, a thin film heater made of helical strips, or a twopiece independent heater with more power supplied to the nozzle where itcontacts the mold. However, the heater disclosed in Hiroyoshi hasseveral significant drawbacks that militate against its application to amold manifold or hot runner nozzle. First, the Hiroyoshi heater is notremovable and thus requires replacement of the entire element when theheater bums out. Second, the heater inefficiently heats the entiremachine nozzle body rather than directly heating the molten resin.Third, the heater cannot provide a profiled temperature gradient acrossthe flow of molten resin, an important feature for managing shear stressin the flow of molten resin. Finally, the thickness of the disclosedheater is 0.5 to 2 mm, which is acceptable for application to the outersurface of the machine nozzle, but intolerable for application to theinterior of a melt channel in a mold manifold or hot runner nozzle.

U.S. Pat. Nos. 5,007,818 and 5,705,793 disclose the use of heaters whichare deposited directly on the flat surface of the cavity mold. U.S. Pat.No. 5,504,304 discloses a removable ceramic heater made of a ceramicpaste whose thickness is hard to control. Such heaters as these do notprovide for intimate contact with the nozzle body or the nozzle tip andthus reduce heat transfer and increase heat loss. Reference also made behad to the following U.S. patents (each of which is incorporated hereinby reference) which disclose heater technology; U.S. Pat. Nos.5,155,340; 5,488,350; 4,724,304; 5,573,692; 5,569,398; 4,739,657;4,882,203; 4,999,049; and 5,340,702.

Accordingly, there is a need in the art for a method and means ofheating a melt channel of a mold manifold and hot runner nozzle in amanner that is efficient in terms of energy, space, and location.

There is an additional need in the art for an efficient method and meansof providing an appropriate amount of heat to each melt channel in acoinjection or multiinjection hot runner nozzle based on the localizedsize and shape of each melt channel and the rheological characteristicsof the resin flowing therein.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide method and apparatusfor efficient heat and flow management of molten resin within the meltchannel of a mold manifold and a hot runner nozzle.

According to one aspect of the present invention, apparatus used inconjunction with an injection molding machine includes a cavity plate, acore plate disposed relative to the cavity plate to define a cavityspace, and a manifold having formed therein an inlet passage forreceiving a flow of molten resin from a nozzle of the injection moldingmachine. A hot runner nozzle is also provided for directing the flow ofmolten resin from the manifold inlet passage to the cavity space. A moldgate is also provided for regulating the flow of molten resin from thehot runner nozzle to the cavity space, the mold gate together with thehot runner nozzle and the manifold inlet passage defining a non-flatmelt channel for directing the flow of molten resin from the nozzle ofthe injection molding machine to the cavity space. An active or passivethin film element is disposed along the non-flat melt channel.Preferably, the thin film element is an active heater in contact withthe molten resin.

According to another aspect of the present invention, apparatus used inconjunction with an injection molding machine includes a mold defining acavity space, and a manifold having formed therein an inlet passage forflow communication with a nozzle of the injection molding machine. A hotrunner nozzle is provided for flow communication with each of the cavityspace and the manifold inlet passage, the hot runner nozzle and themanifold inlet passage together defining a melt channel. A plurality ofactive or passive thin film elements are intermittently disposed alongthe melt channel.

According to a further aspect of the present invention, apparatus fordirecting a flow of molten resin from a nozzle of an injection moldingmachine to a cavity space defined by a mold includes a manifold havingformed therein an inlet passage for receiving the flow of molten resinfrom the nozzle of the injection molding machine. A hot runner nozzle isprovided for directing the flow of molten resin from the manifold inletpassage to the cavity space, the hot runner injection channel andmanifold inlet passage together defining a melt channel. An active orpassive thin film element is disposed within the melt channel.

According to yet a further aspect of the present invention, apparatusfor directing a flow of molten resin-supplied by an injection moldingmachine to a cavity space defined by a mold includes a hot runner nozzlehaving a plurality of melt channels for directing the flow of moltenresin supplied by the injection molding machine to the cavity space. Aplurality of active/passive thin film elements is disposed substantiallyadjacent to each melt channel for supplying heat to the flow of moltenresin within that melt channel.

Yet a further aspect of the present invention includes apparatus to beused in conjunction with an injection molding machine. A cavity plate isprovided, and a core plate is disposed relative to the cavity plate todefine a cavity space. A hot runner nozzle is provided and includes aplurality of melt channels, each melt channel directing one of multipleflows of molten resin supplied by the injection molding machine to thecavity space. An active or passive thin film element is disposed alongeach melt channel.

According to a further aspect of the present invention, a method ofinjection molding includes the steps of injecting molten resin into amelt channel defined by a manifold and a hot runner nozzle, anddisposing an active or passive thin film element along the melt channelfor heating the molten resin.

These and other objects, features, and advantages can be betterappreciated with reference to the following drawings, in which likereference numerals refer to like elements throughout.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is described in conjunction with the accompanyingdrawings, in which:

FIG. 1(a) is an axial cross sectional view of a circular melt channel ofa mold manifold;

FIG. 1(b) is a longitudinal cross sectional view of the melt channel ofFIG. 1(a) schematically depicting the velocity profile of the resin asit flows through the melt channel;

FIG. 1(c) is a longitudinal cross sectional view of the melt channel ofFIG. 1(a) schematically depicting the shear stress profile of the resinas it flows through the melt channel;

FIG. 1(d) is a cross sectional view of a manifold, including a networkof melt channels, schematically depicting variations in the shear stressprofile of the resin as it flows through the manifold;

FIG. 2(a) is a graph showing the relation between temperature andviscosity at a constant shear rate;

FIG. 2(b) is a graph showing the relation between shear rate andviscosity at a constant temperature;

FIG. 2(c) is a longitudinal cross sectional view of a melt channelshowing the velocity of a flow of resin as it rounds a corner in themelt channel;

FIG. 2(d) is a longitudinal cross sectional view of a melt channelshowing boundary layers formed therein by a flow of resin;

FIG. 3 is an elevated perspective view of a mold manifold showing aplurality of 90° turns;

FIG. 4(a) is a schematic representation of a mold manifold;

FIG. 4(b) is a series of axial cross sectional views of the moldmanifold of FIG. 4(a) showing uneven formation and distribution ofboundary layers;

FIG. 5 is a longitudinal cross sectional view of a three-material,five-layer PET preform showing incomplete penetration of one of thelayers, a phenomenon known as DIP;

FIG. 6 is a schematic cross section of a high cavitation mold comprisingthin film manifold and hot runner heaters in accordance with anembodiment of the present invention;

FIG. 7(a) is a schematic cross section showing the layers of thin filmelements in the thin film heater 62 of FIG. 6;

FIG. 7(b) is a schematic cross section showing the layers of thin filmelements in the thin film heater 65 of FIG. 6;

FIG. 8(a) is a cross sectional view of an improved hot runner nozzledesign in accordance with another embodiment of the present invention;

FIG. 8(b) is a chart showing the lack of temperature drop in the upperportion of the hot runner nozzle;

FIG. 9 is a cross sectional view of an improved nozzle tip and mold gateinsert in accordance with an yet another embodiment of the presentinvention;

FIG. 10 is a schematic cross sectional view of the nozzle tip shown inFIG. 9;

FIG. 11 is a cross section of the components of the FIG. 9 nozzle;

FIG. 12 is a cross sectional view of a coinjection nozzle comprisingthin film heaters in accordance with another embodiment of the presentinvention;

FIG. 13 is a cross sectional view of a molding machine includingshooting pots and comprising thin film elements within the shooting pot;

FIG. 14(a) is an axial cross sectional view of a melt channel having athin film heater removably attached to its outer periphery;

FIG. 14(b) is an axial cross sectional view of a melt channel having athin film heater removably attached to its inner periphery;

FIG. 15 is a schematic cros sectional view of a molding machine havingboth a valve gate and a thermal gate;

FIG. 16(a) is a schematic cross section of a valve-gated nozzle having athin

film heater;

FIG. 16(b) is a schematic view of the thermocouple on the end of thevalve

stem of FIG. 16(a);

FIG. 17 is a schematic cross section of the film heater of FIG. 16(a);

FIG. 18(a) is a schematic cross section of a nozzle tip having internaland

external film heaters;

FIG. 18(b) is an end view of the film heater on the tip of the nozzle ofFIG. 18(a);

FIG. 19(a) is a schematic cross section of a nozzle plug having aninternal

film heater;

FIG. 19(b) is a schematic cross section of a nozzle plug having anexternal

film heater;

FIG. 20 is a schematic cross section of a manifold and nozzle which have

film heaters;

FIG. 21(a) is a schematic cross section of a mold gate insert having afilm

heater;

FIG. 21(b) is a schematic cross section of a mold gate sleeve having afilm

heater;

FIG. 22 is a schematic cross section of a mold plug having a film heaterwith different widths;

FIG. 23(a) is a schematic view of the resistive patterns on a thin filmheater:

FIG. 23(b) is a schematic view of the resistive patterns on another filmheater;

FIG. 23(c) shows a film heater disposed inside a melt channel; and

FIG. 23(d) shows a film heater disposed on the outside of a meltchannel.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

I. Introduction

The advantageous features of the present invention will be describedwith respect to a plastic injection molding machine utilizing thin filmheater and sensor technology. Of course, the invention is not limited tosuch embodiments, but may be applied in any molding technology withinthe scope of the attached claims.

As described below, an injection molding system according to the presentinvention may include electrical heaters and temperature sensors tobetter manage and control the flow of the molten resin between in theinjection machine nozzle and the mold cavity space. Thus, the presentinvention may comprise active and/or passive film elements which may bedeposited directly on the surface of the mold elements (such as in themanifold and/or adjacent the mold gate area) to precisely manage thetemperature profile in the moving, molten resin. For some applications,these film elements may be deposited directly on the nozzle housingand/or the nozzle tip, on a runnerless probe, on a valve stem, or on asurface of a mold gate insert. In other cases, the film elements may bedeposited on a removable heater plug which is located at one or morepredetermined positions in the molding system. Preferably, the activefilm element comprises a film heater, and the passive film elementcomprises a thermal sensor (e.g., a thermistor or thermal couple) and/ora pressure sensor. The film elements may be single layer elements, butpreferably comprise a sandwich of several film layers having differentelectrical, thermal, and wear characteristics. One film layer willusually be made of an electrically highly-resistive material. Dependingupon the particular molten-resin and the particular molding processcharacteristics, the film can be either a “thin” or “thick” elementwhich is preferably deposited using chemical deposition, vapordeposition, film spray techniques, or equivalents thereof. The filmheating and sensing elements may also comprise flexible substrates whichare trimmed and installed, as needed, at any location in the injectionmolding machine.

Also within the scope of the present invention is the use of such filmelements in conjunction with the known heaters described above. Bycarefully selecting the appropriate film heating elements (when used inconjunction with or in place of known heaters) fine adjustments may bemade to the molten resin temperature gradient and profile to provideprecise heat flow control. Such precise control can be effected beforethe molten resin enters the heated space, thus providing constant (orprecisely-managed) viscosity and velocity of the melt flow.

If the film heater is directly deposited, this can also eliminate theair gap between the heater and the heated surface thus providingintimate and direct contact for improved temperature transfer betweenthe heater and the heated surface, to achieve energy savings and longerheater life. Also, the direct deposition of the film heater makes themold elements themselves simpler to design and manufacture since theymay be made smaller and more energy efficient and use less space withinthe mold machine itself. Furthermore, the quality of the molded articlesis significantly improved because of the precise management of the heatflow in the injection molding machine. Additionally, when molding anarticle that has several resin layers deposited at once, the use of filmheater elements will allow each layer to having a uniform thickness andlength. In the case of molding PET preforms using the film heatersdescribed below, the acetaldehyde level is lower and is more uniformlydistributed across the cavities of the multi-cavity mold. This isbecause the film heaters are located adjacent the melt channels and canbe individually controlled and activated so that the temperature is veryuniform across the entire manifold.

Also, by improving the heating control at the mold gate area, the spruegate (vestige) of the molded preform may be made very small withsubstantially no crystallinity penetrating the preform wall.

Further, the use of the film heaters according to the present inventionwill provide significant advantages when molding two different colorresins through the same nozzle. Precise heat control will allow anabrupt transition between the different colors, increasing the qualityof the final product and reducing wastage.

Thus, the film heaters according to the present invention are inintimate contact with the surface to be heated, and can provide fasterheating response time, lower temperature inertia, are small enough to beplaced in many different areas of the mold, and can provide a tightlyconstrained temperature profile which leads to faster molding, higherquality in the produced articles, smaller machine parts, reduced energyconsumption, and longer machine life.

By utilizing film sensors according to the present invention, moreprecise temperature management and control of the entire process can beachieved. Such film sensors can be placed in many more locations thanknown thermal couples, and are easily installed, maintained, andmonitored. Therefore, process feedback and control is also enhancedaccording to the film sensors of the present invention.

2. Preferred Embodiments of the Present Invention

The present embodiments locate compact active and/or passive filmelements along a melt channel from, for example, a sprue bushing to amold cavity space to improve heat and flow management therein. Theactive elements, which may be fabricated using advanced thin filmtechnologies, are compact, reliable, stable, and energy efficient.Advantageously, the active elements may be located near or in directcontact with a flow of molten resin. The active elements may be any of athin film heater, thermistor, thermocouple, resistance temperaturedetector, pressure sensor, gas sensor, optical guide leakage sensor, orcombinations and equivalents thereof. The passive elements, which alsomay be fabricated using thin film technologies, interact with the activeelements and may be made of electrical and thermal insulative materialsand/or wear resistant materials. Preferably, the passive elements are indirect contact with the flow of molten resin to improve the laminar lowthereof. Employing these thin film elements optimizes heat managementand overall control of the injection molding process. In particular, thethin film elements may directly heat the resin in the manifold or hotrunner nozzle according to local and customized needs. Further, the useof thin film elements favorably impacts material selection and componentsize along the melt channel.

The present embodiments also provide an innovative mold controller andlogic operation means either coupled to or embedded in the mold. Themold controller and logic operation means are physically independentfrom, but in communication with, the controller and microprocessor ofthe injection molding machine. In this regard, reference is made to U.S.Pat. No. 5,320,513 issued to Schmidt, assigned to the assignee of thepresent invention, and incorporated herein by reference. Schmidtdiscloses a mold integrated circuit board that connects the hot runnernozzle heaters and temperature sensors to the machine controller via aconnector. According to the present embodiments, the printed circuitboard of the mold disclosed by Schmidt further carries control and logicsignals generated by a mold controller and/or a mold microprocessor.Thus, the end user of the mold will better be able to handle theprocessing parameters of the mold in conjunction with various injectionmolding machines. The mold-machine interface will allow either the mold,the machine, or both to be tuned for specific injection moldingprocessing conditions. Also, the interface will reduce the complexity ofthe injection molding controls. Communication between the moldcontroller and the-machine-controller and/or between the active thinfilm elements and the mold controller may be accomplished by eitherwired or wireless means, with the latter further reducing the complexityof the wire connections.

Mold heat management and process control depend on the specificapplication, the type of resin used, the mold manifold and hot runnernozzle design, and the number of mold cavities. The present embodimentscould be applied to improve heat management and process control inseveral molding processes, three of which processes relate to highcavitation molding and, more particularly, to injection molding ofblowable PET preforms.

A first application of the present invention reduces and more uniformlydistributes acetaldehyde (“AA”) inherently generated in a mold duringthe injection process. European Patent Application 293 756 A2 by Halar,et al., filed by the assignee of the present invention and incorporatedherein by reference, thoroughly discusses the problems associated withAA formation. According to Halar, et al., a high level of AA isgenerated by non-uniform thermal degradation of PET as it flows throughmanifold channels. This phenomenon is demonstrated in FIGS. 1(a), 1(b),and 1(c), in which the velocity profile 20 and the shear stress profile24 are schematically depicted for the flow of resin through a channel 22of a mold manifold. Due to the melt channel profile 26, the resin flowsfaster at the center of the channel where the shear stress is minimum,thus forming boundary layers that are symmetrical across the flow. Thetemperature profile is similar to the shear stress profile, i.e., thetemperature of the resin is minimum at the center of the channel. Inmost molding applications, however, the resin flow does not follow astraight path, as shown in FIGS. 1(b) and 1(c), but rather makes one ormore angular turns through a series of branch channels thatsimultaneously feed a plurality of cavity spaces (see FIG. 3). Asindicated in FIG. 1(d), when the resin flow through one channel 21 isdiverted 90° into several branches, such as the first two channels 27and 29, the velocity, shear stress, and temperature profiles becomeasymmetrical as the resin flows slower around the inner corner 23 thanthe outer corner 25. At this stage, the shear stress and temperaturevalues 30 are higher near the inner corner 23 than the values 28 nearthe outer corner 25. This asymmetrical behavior further is enhanced andreduced respectively when the flow again is diverted into channels 31and 33. Not only are shear stress and temperature profiles 32 and 36asymmetrical but they are also different from one another.

Halar, et al. teaches that different asymmetrical profiles in differentmelt channels of a high cavitation mold cause AA differences in moldedparisons. According to Halar, et al., the AA level can be minimized andmade more uniform by providing static mixers within the melt channels ofthe mold manifold. Unfortunately, however, the static mixers induce apressure drop and an increase in shear stress. U.S. Pat. No. 5,421,715issued to Hofstetter, et al. discloses the use of static metallicelements called spokes in the manifold channels to create turbulence andhomogenize the temperature distribution across the flow, thus reducingthe AA level. The spokes of Hofstetter, et al. are no different than thestatic mixer of Halar, et al. and thus do not represent the idealsolution. In summary, providing mechanical obstructions within the meltchannel may more uniformly redistribute the AA level among the injectioncavities, but doing so creates additional problems.

A second application of the present invention promotes more uniformfilling of high cavitation molds by suppressing the thermal andviscosity boundary layers that typically form when a flow abruptlychanges direction. FIGS. 2(a) and 2(b) depict the temperature versusviscosity and shear rate versus viscosity graphs for a typical moltenresin. As shown in FIGS. 2(c) and 2(d), an inner layer 40 is hotter andmoves at a slower velocity than the middle and outer layers. If amanifold feeds several cavities, as shown in FIG. 3, the formation ofboundary layers will cause asymmetrical temperature, shear stress, andvelocity profiles for the flow of resin for each cavity, as shown inFIGS. 4(a) and 4(b). This problem also mentioned by Halar, et al., maybe solved by using a “melt flow redistributor” such as that disclosed inco-pending U.S. patent application Ser. No. 08/570,333 by Deardurff, etal., assigned to the assignee of the current invention and incorporatedherein by reference. The “melt flow redistributor” is located after a90° turn in a melt channel. Thus positioned, this device redirects theouter boundary layer of resin, which is more thermally degraded that thecentral layer, in a balanced proportion among several melt channels.Because this device works differently than a static mixer, it does notinduce a pressure drop. However, the “melt flow redistributor” isrelatively difficult to assemble and service.

A third application of the present invention, derived from the secondapplication, combats a phenomenon known as dip. The dip is an uneven orunfilled portion within a coinjected layer. FIG. 5 illustrates the dipphenomenon occurring in a typical three-material (A-B-C) five-layer(A1-A2-B1-B2-C) PET preform 46. A dip of length L appears in the neckportion N of the preform 46. Three resins A-B-C are either sequentiallyor simultaneously coinjected using conventional injection means to forma five-layer blowable preform. The dip is unacceptable because one resin(usually the barrier) does not fully fill the space in the neck areapartially occupied by the other resin (virgin, etc.). The dip isbelieved to be caused by the formation of boundary layers within amanifold. These boundary layers cause non-uniform temperature andviscosity profiles across a flow of molten resin, which in turn causesdip. The dip may be improved by providing static mixers within the meltchannels, but as mentioned previously, such static mixers createadditional problems.

The present invention overcomes the AA, non-uniform filling, and dipproblems by replacing or supplementing conventional coil or band heaterswith film heaters strategically disposed along the melt channels andindividually controlled to provide the desired heat profile. Forexample, thin film heaters placed adjacent to each corner 23 can becontrolled to provide more heat to the resin flow than thin film heatersplaced adjacent zone 22 of the melt channels in order to provide aconstant temperature profile throughout the melt channel. Thus located,the thin film heaters can change the velocity, temperature, and shearstress profiles of the flowing resin according to the specific geometryof each melt channel and angle of intersection with adjoining meltchannels.

A fourth application of the present invention relates to variousimprovements of current injection molding components that, in mostinstances, do not provide an optimum temperature profile in a flowbefore the molten resin enters the mold cavity space. Examples of suchcomponents that would benefit from application of the present inventioninclude coinjection hot runner nozzles, edge gating nozzles, tips ofinjection nozzles, nozzle-manifold interfaces, rim gating nozzles, moldgate inserts, etc.

Improved components embodying film heaters and insulation layers willnow be discussed with reference to several U.S. patents, each of whichis assigned to the assignee of the present invention and incorporatedherein by reference.

FIG. 6 is a schematic cross section showing a high cavitation mold spruebushing 62, manifold 64, and hot runner nozzles 66 which are heatedusing thin film heaters 63, 65, and 67, respectively. Each thin filmheater comprises an active film made of a thin film, electricallyconductive material sandwiched between assorted passive thin filmmaterials. If the thin film heater is internally located so as todirectly contact the molten resin, the thin film heater 62 may comprise(as shown in FIG. 7(a)), in order starting from the channel, a wearresistive film 72, an electrically insulative film 74, the electricallyresistive heater film 76, another layer of electrically insulative film78, and finally a thermally insulative film 79. If the thin film heater65 is externally located (as shown in FIG. 7(b)), the wear resistivefilm may be omitted. Likewise, in some applications the thermallyinsulative film may be omitted.

FIG. 8(a) shows an improved design of an injection mold in which themanifold 80, manifold bushing 82, and hot runner nozzle 84 areindividually heated using thin film electrical heaters 81, 83, and 85,respectively. Because a thin film heater 87 may be located inside thenozzle body and in contact with the molten resin, no temperature dropoccurs in the upper portion A of the hot runner nozzle, as shown by thebroken line in FIG. 8(b).

FIG. 9 shows an improved design of a hot runner nozzle tip in accordancewith an embodiment of the present invention. Active and passive thinfilm elements are located inside the hot runner nozzle body 90 along themelt channel 92 and in close proximity to the mold gate area 94. Theactive thin film elements are heaters 91, 93, 95, and 97 for maintainingthe resin at an optimum temperature. Apart from compactness and energysavings, the thin film heaters confer several other significantadvantages. For example, the thin film heaters are easy to locate inareas that are not accessible to coil heaters, such as in the immediatevicinity of the mold gate.

In the illustrated embodiment, the thin film heaters 95 are locatedalong diverter channels of the nozzle tip. The thin film heaters 97 mayalso be located on the inner periphery of the mold gate insert 98 inorder to heat the mold gate more effectively. Locating thin film heaterswithin the mold gate insert provides additional advantages with respectto “color change” preparation. As is generally known in the art, whenchanging resins to mold an identical piece but of a different color, oneshould “flush” the first resin from the nozzle channels. By locating athin film heater 97 on the inner periphery of the mold gate insert, theinsert may be heated to facilitate flushing of the gate channel. Also,heaters may be combined with thermocouples as shown at 97 and 99.

The mold gate insert further may comprise a thin film pressure sensor 96and/or thin film temperature sensors (not shown). FIG. 10 shows thedisposition of pressure sensors 96 and thermocouple 100 around thenozzle tip 90°. As shown in FIG. 11, the individual components of thehot runner nozzle and mold gate insert are easily removed, manufactured,and serviced.

FIG. 12 shows a coinjection nozzle with thin film heaters in accordancewith yet another embodiment of the present invention. At least one thinfilm heater may be disposed around or inside the housing of eachcoinjection channel to better control the temperature of each resin. Inthis embodiment, a three channel nozzle is shown wherein the channel 110carries resin A, channel 112 carries resin B, and channel 114 carriesresin C. The valve gate stem 116 selectively shuts off communicationbetween the nozzle channels and a cavity space 118. Thin film heaters111, 113, and 115 are respectively located inside the channels. However,for certain applications it may be possible to use only two heaters,with one heater heating two channels if the wall between the twochannels is thin and/or thermally conductive. For example, in FIG. 11heater 111 may be sufficient to heat both resins A and B. Because thethin film heaters will directly contact the flow of molten resin, a wearresistive film may be provided directly adjacent to the flow.

FIG. 13 shows a molding machine including shooting pots 120 for meteringthe amount of resin delivered to the hot runner nozzle 122. Shootingpots are typically used when injecting parts that must meet stringentweight requirements, such as the accurately measured layers commonlyrequired for a coinjection mold. In accordance with the presentinvention, thin film heaters 121 is located in the shooting pot area toheat the shooting pot area independently from other thin manifoldheaters such as heaters 123, 125 disposed on manifold 124. Additionally,thin film thermal sensors may be located in the shooting pot area.

FIGS. 14(a) and 14(b) show preferred means for removably attaching athin film heater to either the outside or the inside of a hot runnernozzle, respectively. The thin film heater is deposited on a flexiblethin, band substrate that may display spring-like characteristics. Athin film heater attached in this manner may be easily replaced in theevent of a failure. In FIG. 14(a), thin film heater 132 is disposedoutside of nozzle 130 and may comprise, for example, electricallyinsulated layer 132, electrically conductive layer 134, and electricallyinsulated layer 136. A connector 138 fits within a channel of the nozzle130 and restrains the two ends of the resilient heater 132. Suchconstruction can provide localized heat to the resin and melt channel139. In FIG. 14(b), the heater 132 is disposed inside nozzle 130 and mayalso comprise the layers 132, 134, and 136. A wear layer (now shown) canalso be provided between layer 132 and the melt channel 139 to presentwear on the heater 132. Of course, the heating elements in layer 134 mayextend only partially around the circumference of the nozzle, and be inany configuration (spiral, planar, stripped, herringbone, annular, etc.Also, the heating elements may extend to different lengths along theaxial direction of the nozzle.

FIG. 15 shows an injection molding machine having both a hot runnervalve gate and a hot runner thermal gate. The molten resin precedes fromthe machine injection nozzle (not shown) through the sprue bushing 150into the manifold 152 and into the melt channel of each nozzle. Themolten resin flowing through the bushing and manifold may be maintainedat the optimum temperature by using well known band or coil electricheaters. The molten resin is then injected through each of the nozzlesinto respective mold cavities 154 and 156. The hot runner valve gate 158has a thin film heater 159 associated therewith to maintain the moltenresin at the precise, desired temperature as it passes through the valvegate 158 into the cavity 154. Likewise, the hot runner thermal gate 157has a thin film heater 155 associated therewith to precisely control thetemperature of the molten resin as it flows into cavity 156.

FIG. 16(a) is a schematic cross-section of a valve gated hot runnernozzle where a film heater is deposited directly on the tip portion ofthe stem, and a film thermocouple is deposited directly on the end ofthe stem. The valve-gated nozzle 160 has a nozzle tip 162 which fitswithin mold plate 164 abutting the mold plate 164′ containing the moldcavity space 166. The movable valve stem 168 has a film heater 167deposited on the outer surface thereof in a pattern, for example, asshown in FIG. 16(a). Preferably, and as shown in FIG. 16(b), athermocouple is deposited on the end of valve stem 168 for accuratetemperature measurement precisely at the valve gate itself.

As shown schematically in FIG. 16(a), the film heater 167 may be coupledto electrical contacts 161 through terminals 163. Likewise, electricalcontacts 165 are disposed to contact terminals 169. The electricalcontacts are coupled to a mold control processor 1000, such as thatdescribed in the Schmidt patent discussed above.

FIG. 17 is a cross-sectional view of the film heater 167 of FIG. 16(a).Closest to the valve stem 168 is a layer 171 made of electricalinsulative material. Next is a layer 173 which comprises theelectrically resistive material forming the heating element. On theoutside is layer 175 which comprises an electrically insulative materialthat also has good thermal transmission characteristics.

FIG. 18(a) is a schematic cross-sectional drawing showing film heater181 disposed on a bottom exterior surface of nozzle tip 180. As shown inFIG. 18(b), the film heater 181 may have a resistive pattern whichsurrounds the melt channels 182 and 183, as shown. The heater terminals184 and 184′ may be connected to electrical contacts (not shown).

The nozzle tip 180 may also have a heater plug 190 (to be describedbelow) which has a film heater 191 disposed on an outer surface thereof.The heater plug 190 is disposed in the melt channel 186 of the nozzletip 180. Both film temperature sensors (not shown), may also bedeposited on any convenient surface of the nozzle tip 180 to monitor thetemperature of the molten resin in the melt channel 186. Preferably, thetemperature sensor is a film thermocouple disposed in direct contactwith the molten resin very close to the mold gate orifice.

Preferably, the nozzle tip 180 includes connectors for the thermocoupleand the heater which are attached to the nozzle body by a fast removalmechanism, such as a bayonet mechanism, which allows rapid assembly andremoval of the tip without having to disconnect any wiring. In someinstances, it is preferable to have two thermocouples placed close toeach other so that if one is broken, the other one is still operative.

FIG. 19(a) is a schematic cross-section of a film heater plug 190 whichis a convenient and easy way to apply film heaters and film sensors tothe melt channels of injection molding machines. Plug 190 comprises ametal plug 192 having a film heater 193 disposed on an interior surfacethereof adjacent the melt channel 194. Preferably, the heater 193comprises an inner wear resistive layer 195, an electrically resistivelayer 196, an electrical insulation layer 196, and a thermal insulationlayer 198. The advantage of such a construction is that the plug 190 canbe made small and replaceably positioned at any point in the meltchannel. The plug can be used at any located in alignment with the meltchannel of the mold, for example, in the manifold, in the hot runnerhousing or in the nozzle tip. The melt channel can be constructedcomplementary structure so that such heater plugs can be placed at anyconvenient location along the melt channel. Moreover, such plugs can belinear, T-shaped, or angled to fit any location along the melt channel.Since it is much easier to dispose a flexible film heater on theinterior surface of a small, replaceable heater plug, the cost ofdisposing that heaters on the inside surface of a long melt channelmanifold (as depicted in FIG. 3) can be avoided.

FIG. 19(b) depicts another embodiment of the heater plug 190 in whichthe heater 193 is disposed on the outer surface 192. In this instance,the inner layer 195′ comprises a dielectric with good thermaltransmitting characteristics, layer 196′ is the electrically resistiveheating element, and layer 197′ is a thermal insulator. In someinstances, a wear resistant layer may be deposited on the outside of thelayer 197′. Likewise, a wear resistant layer 198′ may be deposited onthe inside of the plug 192 to enhance resistant to the wear of themolten resin.

FIG. 20 shows the application of removable heater plugs 201 and 202within an injection molding machine. Heater plug 201 has film heater 203on the exterior surface thereof and is disposed within manifold 204,which, for example, may also be heated by conventional manifold heater205.

The heater plug 202 is disposed within nozzle head 206 and nozzle body207 and has a wear resistant layer (sleeve) 208 disposed on an interiorsurface thereof adjacent the melt channel 209. A film heater 210 isdisposed on an exterior surface of the heater plug 202 adjacent thenozzle tip 211. The nozzle housing 212 is preferably made of a thermalinsulation material. The heater plugs 201 and 202 are preferably made ofa highly thermally conductive material such as CuBe. Since the heaterplugs 201 and 202 are modular and removable, they may be easily replacedfor repair or for the molding of different types of plastic resin.

FIG. 21(a) is a schematic cross-section of a mold gate insert 210 havingan internal film heater 211 disposed on an inside surface adjacent thenozzle tip (not shown) and the mold gate orifice 212. Since the moldgate insert 210 is removable, a connector 213 is disposed on a surfacethereof to carry the electrical contact wires to the film heater 211.The connector 213 will mate with a like connector in the nozzle housingor the mold plate (not shown) so that the entire mold gate insert 210 isquickly and easily replaceable.

FIG. 22(b) is a schematic cross-section of a mold gate sleeve 215wherein the mold gate body 216 has a film heater 217 disposed on the oneor more of the outer surfaces thereof. Again, since the mold gate sleeveis easily replaceable, it is simple to replace a defective heater or tochange the heating capacity of the heater for different types of resin.

FIG. 22 is a schematic cross-section of a heater plug 220 having a filmheater disposed on the outer surface thereof. However, the film heaterlayer as different thicknesses in areas A, B, and C to provide anengineered temperature profile, as depicted in the left-hand portion ofFIG. 22. This may be used, for example, in molding applications whereportions A and C are located adjacent mold plates which are cooledduring the molding process. This way, the molten resin flowing withinthe melt channel 222 will be maintained at a constant temperature. Notethat in this embodiment, a high wear resistive sleeve 223 is disposed onthe interior surface of the heater plug 220.

FIG. 23(a) is a schematic view of a thin film heater according to thepresent invention having two rectangular patterns of heating elements.Heater 231 has an element with a length L and a pitch P1. Heater 232 hasa heating element with the same length L, but with a different pitch P2.Thus, the same thin film element may provide different heatingcharacteristics to contiguous areas of the melt channel. The contactterminals have a length Lt and a width T adapted to easily engageelectrical contacts on the melt channel structure where the heater is tobe mounted.

FIG. 23(b) is a schematic of a heater having a serpentine shaped heatingelement 235 with contact terminals at different ends thereof.

FIG. 23(c) shows a film heater bent so as to be disposed on the insideof a melt channel, and FIG. 23(d) shows such a heater bent on theoutside of a melt channel.

The following materials, deposition technologies, and patterning methodsare recommended for the various layers used to manufacture the compoundfilm heater deposited directly on the mold elements or on a film heaterplug (the thickness of these layers varies from less than 5 microns andup to 2-3 millimeters):

electrical resistive materials: TiN; tungsten, molybdenum, gold,platinum, copper, TiC, TiCN, TiAIN, CrN, palladium, iridium, silver,conductive inks

electrical insulative materials: beryllium oxide; see also the materialsdisclosed in the U.S. Pat. No. 5,653,932 and U.S. Pat. No. 5,468,141both herein incorporated by reference.

wear resistance materials: titanium, titanium alloys, chrome,electroless nickel, also see the materials disclosed in the U.S. Pat.No. 5,112,025 herein incorporated by reference.

deposition technologies: ion plating, sputtering, chemical vapordeposition (CVD), physical vapor deposition (PVD), flame spraying.

film patterning methods: etching through a mask; laser removal; wiremasking, mechanical removal,

Example for the Heat Requirement: Wattage Density 40-80 W/square inch at240 V

See FIG. 13

Zone A: 37 mm 150 W (tip)

Zone B: 75 mm, 50W (center)

Zone C: 34 mm 100 W (head)

One or several heaters

Patterning: laser removal; lathe; mask wire, etching

Deposition: sputtering

Materials: platinum, tungsten, Molybdenum

Film Sensors for Molding Applications.

Film temperature sensing elements have been disclosed in, for example,U.S. Pat. No. 5,215,597 issued to Kreider, U.S. Pat. No. 5,573,335issued to Schinazi, NASA Report E-7574 of February 1993 by R. Holandaand NASA Report E-9080 of August 1994 by L.C. Martin et al., all ofwhich are all incorporated herein by reference.

Any film temperature sensing device, such as thermistors, othersemi-conductor based devices, or resistance temperature detectors (RTD)are encompassec by the scope of the current invention. Reference is madein this regard to U.S. Pat. No. 4,968,964 issued to Nagai et al., andthe Platinum Resistance Temperature Detector (P-RTD) Catalogs of Heraeusthat are incorporated herein by reference. The current invention alsoencompasses a thin film RTD as another preferable alternative to a filmthermocouple, because it offers the advantage of being made of a singlethin film material that is easier to deposit and etched.

According to the current invention, it is preferable to select thematerials for the film thermocouple that meet the current thermocouplestandards (such as ANSI), and that can be deposited on the support baseof the mold part. Accordingly, a major design target for the filmthermocouple is to select two dissimilar materials for the wires thatare either identical or close to the resistive material of the thin filmheater. The following commercial data published by Insulation Seal Inc.and SRS Corp. show the material selection and characteristics forseveral standard thermocouples that can be also used as guidelines tomanufacture film thermocouples.

ANSI Thermocouple Pair TC Temperature Medium Std. Type Materials &Polarity (max.) Error T Copper (+)  350° C. Constantan (−) J Iron (+) 750° C. +/−2.2° C. Constantan (−) E Chromel (+)  900° C. +/−1.7° C.Constantan (−) K Chromel (+) 1250° C. +/−2.2° C. Alumel (−) R Platinum13% Rhodium (+) 1450° C. +/−1.4° C. Platinum (−) S Platinum 10% Rhodium(+) 1450° C. +/−1.4° C. Platinum (−) C Tungsten 5% Rhenium (+) 2320° C.Tungsten 26% Rhenium (−) B Platinum 30% Rhodium (+) 1700° C. +/−4.4° C.Platinum 6% Rhodium (−)

According to the current invention, the film thermocouple is made usingwell known microlithographic techniques that insure a very highdimensional accuracy, excellent adhesion of the themocouple to thesubstrate and connection between the two dissimilar materials. Anotheradvantage of the micro lithographic technique is that a batch ofthermocouples can be simultaneously manufactured in order to ensure thatthe thickness of the deposited alloy is the same for several temperaturesensing elements that will be mounted in a high cavitation mold. Anotheradavantage is that, with no extra cost and within the same space, a“back up” or a reference thermocouple can be actually deposited close tothe actual thermocouple. In this manner, if for whatever reason thecurrent thermocouple fails to respond, the back up can be activated,without interrupting the molding process or servicing the mold.

In a preferred embodiment, a thin film (R-class) thermocouple is made ofPlatinum-13% Rhodium and Platinum and is manufactured in a class 1000Clean Room using the well known sputtering process. Depending on thelocation of the thin film wires to the lead wires connections are madeusing the well known parallel-gap welding process. This thermocouple canbe located anywhere along the melt channel as it can withstandtemperatures in excess of 1,000° C.

Thus, what has been described is unique structure and function wherebyheating, sensing, and melt control in a molding machine may besimplified, made easy to replace, and may be customized and to providemolded articles more quickly, less expensively, and with higher quality.

While the present invention has been described with respect to what arepresently considered to be the preferred embodiments, it is to beunderstood that the invention is not limited to the disclosedembodiments. To the contrary, the invention is intended to cover variousmodifications and equivalent arrangements included within the spirit andscope of the appended claims. The scope of the following claims is to beaccorded the broadest interpretation so as to encompass all suchmodifications and equivalent structures and functions.

We claim:
 1. An injection molding nozzle heater, comprising: a firstdielectric layer; a resistive heating element on the first dielectriclayer; two electric terminals in electrical communication with theresistive heating element; and a second dielectric layer applied overthe heating element.
 2. The heater of claim 1, further comprising aninjection molding nozzle, and wherein the first dielectric layer isapplied directly onto a surface of the nozzle.
 3. The heater of claim 1,wherein the first dielectric layer is on an outer surface of the nozzle.4. The heater of claim 1, wherein the heating element is disposed in aspiral pattern.
 5. The heater of claim 1, wherein the heating element isa film applied in a pattern about a circumference of the firstdielectric layer.
 6. The heater of claim 5, wherein the patterncomprises one of a spiral, a planar, a striped, a herringbone, or anannular pattern.
 7. The heater of claim 1, wherein the heating elementis formed using conductive ink.
 8. The heater of claim 7, wherein theheating element is applied in a pattern about a circumference of thefirst dielectric layer.
 9. The heater of claim 8, wherein the patterncomprises one of a spiral, a planar, a striped, a herringbone, or anannular pattern.
 10. The heater of claim 1, further comprising atemperature sensor in contact with the nozzle.
 11. The heater of claim10, wherein the temperature sensor is a film sensor.
 12. An injectionmolding nozzle, comprising: a metal nozzle body; a first electricallyinsulative layer on the nozzle body; a resistive heating element on thefirst electrically insulative layer; electric terminals in electricalcommunication with the resistive heating element; and a secondelectrically insulative layer applied over the heating element.
 13. Thenozzle of claim 12, wherein the first electrically insulative layer isdirectly applied on an outer surface of the nozzle body.
 14. The nozzleof claim 12, wherein the heating element is disposed in a spiralpattern.
 15. The nozzle of claim 12, wherein the heating element is afilm formed using conductive ink.
 16. The nozzle of claim 15, whereinthe heating element is formed in a spiral pattern.
 17. The heater ofclaim 1, further comprising a cylindrical heat-conducting substrateadapted to be placed, in use, over an outer surface of an injectionmolding nozzle, and wherein the first dielectric layer is on an outersurface of said substrate.
 18. The heater of claim 17, wherein theheating element is disposed in a spiral pattern.
 19. The heater of claim17, wherein the heating element is a film deposited in a pattern about acircumference of the first dielectric layer.
 20. The heater of claim 19,wherein the pattern comprises one of a spiral, a planar, a striped, aherringbone, or an annular pattern.
 21. The heater of claim 17, whereinthe heating element is formed using conductive ink.
 22. The heater ofclaim 21, wherein the heating element is deposited in a pattern about acircumference of the first dielectric layer.
 23. The heater of claim 22,wherein the pattern comprises one of a spiral, a planar, a striped, aherringbone, or an annular pattern.
 24. An injection molding nozzleheater for heating a nozzle, comprising: a cylindrical heat-conductingsubstrate adapted to be placed, in use, over an outer surface of thenozzle; a first dielectric layer on an outer cylindrical surface of saidsubstrate; a conductive-ink resistive heating element on said firstdielectric layer, said heating element being formed in a pattern andarranged, in use, to cause heating of the nozzle through the substrate,said heating element having contact terminals arranged to support anelectrical connection to the heating element; and a second dielectriclayer extending over said heating element, but not covering the contactterminals, thereby permitting, in use, coupling of the heater element toan electrical supply.
 25. The heater according to claim 24, wherein saidheating element is arranged in a spiral pattern.
 26. The heateraccording to claim 24, wherein said second dielectric layer comprises anelectrically insulating and mechanically protective layer.
 27. Theheater according to claim 24, wherein the conductive-ink resistiveheating element is a thick-film.
 28. The heater according to claim 24,wherein the cylindrical heat-conducting substrate displays spring-likecharacteristics.
 29. The heater according to claim 24, wherein theconductive-ink resistive heating element is formed by a layer having aplurality of thicknesses engineered to provide, in use, a temperatureprofile within the resistive heater.
 30. The heater according to claim24, wherein the resistive element contains a plurality of contiguousfilm elements having different pitches that generate, in use, differentheating characteristics.
 31. The heater according to claim 24, furtherincluding a temperature sensing element coupled to the dielectric layer.32. The heater of claim 31,wherein the temperature sensor is a filmsensor.
 33. An injection molding hot runner nozzle heater located, inuse, on an outer surface of the nozzle, the nozzle heater comprising: adielectric layer located on the outer surface of the nozzle; a resistiveheater formed by a film layer on said dielectric layer, the film layer aconductive ink disposed in a pattern on the dielectric layer; aninsulative layer covering said heater layer; and two electrical contactsin contact with said resistive heater and accessible through theinsulative layer.
 34. An injection molding hot runner nozzle heaterlocated, in use, on an outer surface of the nozzle, the nozzle heatercomprising: a dielectric layer located on the outer surface of thenozzle; a resistive heater formed by a patterned film layer disposed onsaid dielectric layer, the film being a conductive ink; an insulativelayer covering said heater layer; and two electrical contacts in contactwith said resistive heater and accessible through the insulative layer.35. The heater according to claim 34, wherein said heater comprises twoheating elements coupled to each other and coupled between theelectrical contacts, said heating elements being disposed in a patternabout a circumference of the dielectric layer and wherein said patterncomprises one of a spiral, a planar, a striped, a herring-bone or anannular pattern.
 36. The heater according to claim 34, furthercomprising a film-based temperature sensor on the outer cylindricalsurface of the nozzle and wherein said dielectric layer and theinsulative layer comprise thick-film layers.
 37. The heater according toclaim 34, wherein the insulative layer is a thermal insulation layer.38. The heater according to claim 34, further comprising awear-resistant layer adjacent the insulative layer.
 39. The heateraccording to claims 34, wherein the dielectric layer is located on aremovable substrate positionable about the outer surface of the nozzle.40. An injection molding nozzle comprising: a metal nozzle body havingan outer cylindrical surface; a film dielectric layer deposited over theouter cylindrical surface; a resistive heater formed by a film-basedlayer deposited in a pattern on a portion of said dielectric layer;first and second electrical contacts deposited on said dielectric layerand in electrical contact with respective first and second ends of saidresistive heater; and an electrical insulation layer deposited over saidresistive heater, but through which electrical insulation layer thefirst and second electrical contacts are contactable.
 41. The nozzleaccording to claim 40, wherein said resistive heater comprises a linearresistive heating element disposed in a spiral pattern, and wherein saidheating element comprises a plurality of layers.